The Wonders of Water

When You Need More

Physical activity, heat, and humidity can increase our fluid needs. In these situations, keep water bottles close at hand and drink frequently to avoid dehydration. If you're going to be physically active for long periods, consider sports drinks that hydrate and provide easily usable sugar and electrolytes.

Illnesses accompanied by increased body temperature, excessive perspiration, vomiting, frequent urination, or diarrhea can also increase our fluid needs. Be sure to drink plenty of liquids if you have one of these conditions, and see a doctor if your fluid losses are excessive or prolonged.

How Much Is Too Much?

Scientists on the IOM panel did not set an upper limit for water.

"Water intoxication is very rare, although it has been seen in fraternity pranks. That can be very serious and result in death" says David Perlow, MD, an Atlanta-based urologist.

One recent study of Boston Marathon runners showed that one in three marathon runners was drinking too much water during a race -- probably because they were following recent advice to drink as much as tolerated.

If you follow your thirst, you won't go wrong, Perlow says. He notes that pre-modern man never ran around sipping on a water bottle. A dry mouth indicated it was time to run to the stream for a drink.

"Trust your thirst instinct to make sure you get enough fluids and, of equal importance, void frequently," suggests Perlow.

Perlow says the bladder is like a balloon. When you make infrequent trips to the bathroom, it can become overstretched -- which can result in problems with incomplete emptying, he explains.

He recommends 7-12 trips to the toilet daily for most healthy people.

Water and Weight Control

For years, drinking water has been recommended for weight loss -- despite the fact that fluids generally satisfy thirst and not hunger. Barbara Rolls, PhD, an expert on thirst and satiety, points out that thirst and hunger are regulated by entirely different mechanisms.

A recent study by Rolls and colleagues at Penn State University looked at whether people who drank water with lunch took in fewer calories than those who drank other low-calorie beverages. They found that drinking water had little effect on total calorie consumption at the meal.

"In all of our research, we have never been able to show that water can cause weight loss," says Rolls. The only way drinking water can help you lose weight is if you substitute it for higher-calorie beverages or foods, she explains.

However, eating foods with high water content can help dieters, by increasing the fullness factor.

"When you add water to a bowl of vegetables as in soup, the soup has greater satiety than when the vegetables are eaten alone with a glass of water," explains Rolls, author of The Volumetrics Eating Plan and The Volumetrics Weight Control Plan. "When water is incorporated into food or shakes, satiety is increased and subjects ultimately eat less food."

The weight loss benefits of water stem from several facts:

• Foods that incorporate water tend to look larger.
• The higher volume of these foods provides greater oral stimulation.
• Most important, when water is bound to food, it slows down absorption and lasts longer in the belly.

If you want to lose weight, Rolls recommends an eating plan that includes plenty of high-volume foods such as fruits, vegetables, broth-based soups, and oatmeal, along with adequate fluids to satisfy your thirst.